5DM3 - shooting RAW since 2013 June, I have never had a problem with the footage. Check your card speed. There are scum on ebay and Amazon selling fake Komputerbay cards. I have heard unconfirmed rumors some KomputerBay 64gigs being defectively slow.
Pro use. Just my opinon, but if you are talking about pro use as in a budget (paid talent, crew, locations) you'd be nuts not to simultaneously use a external HDMI recorder. You cannot review your takes in RAW, and the external HDMI gives you usable backup if there is some type of problem. Same with locations or events you cannot re-shoot quickly and for free. For casual, non-budgeted shoots, I usually leave the Ninja at home, but I would never, ever, not use it on something that would cost me money or time for a re-shoot.